Oscillation generator and modulator



Oct. 16, 1928. v1,687,882

v H. w. NlcHoLs 'OSCILLATION GENERATOR AND MODULATOR by ,my

Patented Oct. 16, 1928.

UNITED STATES PATENT oFF-ICE.

HAROLD W. NICHOLS, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR T0 WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW Yong.

OSCILLATION GENERATOR AND MODULATOR.

Application illed Narch 31, 1923. Serial N0. 029,033.

This invention relates to methods of and means for producing and controlling elect-ric oscillations.

One object of the invention is to produce or amplify oscillations at high efficiency, and at a higher degree of efficiency, when employing a variable impedance device, than has previously been known in theart.

Another object of t-he invention is to produce modulated waves at high eficiency.

It is known that for the most eiiicient production of waves by a variable impedance device in a direct current circuit, for example, an amplifier of the space current type, itis essential that the space current through the amplifier tube vary from a minimum to a maximum value and vice versa in Ia sudden or impulsive manner. v

In accordance with the present invention, oscillations are generated impulsively by an amplifier or power tube of the space current type. A highly negative polarizing potential on the grid of the tube normally opposes the transmission of any substantial amount of space current through the tube. A feed back circuit coupled between the output and input circuits ofthe powertube includes therein an auxiliary relay tube of the space current type, the grid of which is provided with a highly (negative polarizing potential so that only the positive peaks of waves impressed thereon are effective in producing space current in the output circuit of the auxiliary tube. ,Said output current, therefore, consists of sharp-non-sinusoidal impulses of space current which are transmitted through the input coupling of the power tube and cause the grid of the power tube to periodically become highly positive for extremely small intervals of time thereby causing very sharp impulses of space current to flow in the output circuit of the power tube, thus producing oscillations in the tuned circuit associated therewith. By using relatively high voltage sources for space current and grid polarization, a very high 'efficiency may be obtained in generating oscillations of a desired frequency. The excitation by a nonsinusoidal impulse permits the amplifier tube to operate with a minimum or very small loss of electrical energy. within the tube as compared to the energy delivered to the output circuit in the form of oscillations of desired frequency.

Modulation of the generated waves in accordance with telephone or telegraph signals may be accomplished by applying the modulating signals to the anode-cathode terminals of the auxiliary relay.

Other object-s of the invention will be apparent from the more detailed .description which follows.

In the drawings, Fig. 1 is a circuit diagram illustrating one embodiment of the invention adapted to generate oscillations and provided with means for modulating said oscillations. Figs. 2 and 3 are graphs indicating the approximate performance of the auxiliary and power tubes, respectively. Fig. 4 is a circuit diagram illustrating a modification of the circuit shown in Fig. 1.

In Fig. 1, a variable impedance device is shown specifically as an amplifier tube 1, of the well known space current type, provided with an input circuit 2 connected between the grid and cathode of the tube and an output circuit 3 connected between the anode and cathode of the tube. The input circuit 2 includes a source 4 for producing a highly negative polarizing potential on the grid of t-he tube. The secondary winding 5 of the transformer 6 is in series with the source 4. The out-put circuit 3 includes in addition to the space current source 7, the variable capacity 8 and primary wind-ing 9 of transformer 10. A distorting device, shown specifically as a relay tube 11 of the space current type, may be an amplifying or non-amplifying distorter. This tube, hereinafter referred to as an auxiliary tube, supplies exciting current to the grid of the power tube 1, and for this purpose may be considerably smaller in power rating than the -power tube. An input circuit 12 is connected between the grid and cathode of tube 11 and an output circuit 13 is connected between the anode .and cathode of said tube. The input circuit 12 includes the source of p0- tential 14, for negatively polarizing the rid of the auxiliary tube 11, and the seconfIary .winding 15 of the transformer 10. The outload 20 may comprise any well known form of load or receiving circuit which utilizes alternating current energy.

The operation of the circuit of Fig. 1 may be understood more clearly by reference to Figs. 2 and 3. The curve 30 of Fig. 2 is the grid voltage-plate current characteristic of the auxiliary tube 11 and shows the Values of space current IB1 as ordinates for different values of grid potential E01, represented as abscissae.

Let it be assumed that the circuit 8, 9 is tuned to resonance with the wave of frequency to be generated and that a current`of said frequency is iiowing therein. An'electromotive force will then be induced in wind ing 15 producing an alternating electromotive force which may be represented as e1. A positive half of such a wave is shown as e, in Fig. 2, the zero axis for the wave e1 being located at a distance es, the potential of source 14, from the zero grid potential point on the curve 30. The wave e, produces a rapid increase in space current IBl. thus producing an im ulse 31 of current through the primary win in 17 of the transformer 6. Inasmuch as e1 ecomes positive only once during each cycle, there will be one impulse IB, and only one for each cycle of the Wave being enerated.

In ig. 3, the curve 32 is the grid voltageplate current characteristic of the power tube 1 and shows the-values of space current IB, as ordinates for different values of grid potential E02 represented as abscissae. The negative polarizing potential ofthe source 4 applied to the grid ofthe power tube 1 is, represented at e4.

The electromotive force e2 is induced in the secondary winding 5 of transformer 6 by the impulse 31 passing through winding 17. It will be noted that the wave e2 applies a much sharper positive peak of potential to the grid of power tube 1 than the sine wave e1 applied to the grid of auxiliary tube 11. As a result of this abrupt change in potential of the grid of tube 1, a space current impulse 33 is produced by the current IEZ- transmitted through the output circuit 3 of the power tube 1. The eii'ect of these sharp impulses upon circuit 8, 9 is to set up and maintain in this circuit free oscillations of the natural frequency of said circuit. The impulses occur at the same point in each cycle of the oscillating current in circuit 8,l 9 and are of such direction as to au ent the oscillating current.

By this method of controlling the power tube 1, it has been found possible to obtain a much higher electrical efficiency in the generation of oscillations than is possible when the grid of the power tube 1 is excited by a sine Wave. Under favorable conditions, it has been found possible to obtain as high as 93% efliciency in converting the energy of the space current source into oscillatory energy of desired frequency in accordance with the method of the present invention` Under the most favorable conditions Where the grid of tube 1 has been excited by a pure sine wave, the highest efiiciency obtained in the output circuit was of the order of 85%, thus showing a marked advantage of the present invention over power circuits in which the grid potential of an amplifier is varied in accordance with a ure sine Wave.

For t e purpose of modulating oscillations produced in the tuned circuit 8, 9, the switch 35, Fig. 1, may be closed to connect the anode-cathode circuit 36 of the modulating tube' 37 of the space current type in parallel with the anode-cathode terminals of the auxiliaryv tube l1. A. source of signal current suchas a voice operated microphone 38 is coupled by means of transformer 39 to the grid circuit 40 of modulator tube 37 to control the space current passing through modulator 37. High frequency choke coil 41 prevents the transmission of impulses of energy from the auxiliary tube 11 to the modulator tube 37, at the same time allowing the signal variations to be transmitted by the modulator tube 37 to the output circuit 13 of auxiliary tube 11. Choke coil 42 and capacity 43 are both of high impedance to waves of signal frequency, that is waves transmitted by the source 38 through the tube 37 Itis thus possible for signal waves to be impressed `upon the anode-cathode circuit of tube 11 without appreciable or objectionable loss by shunting through choke coil 42 and capacity 43. Capacity 43 is at the same time suiiiciently large to present a relatively small or negligible impedance to the passage therethrough of impulse 31.

Waves transmitted from the source 38 vary the potential of the grid in modulator 37' thereby varyin the potential difference between the ano e-cathode terminals of the tubes 11 and 37. The peak values of successive`space current impulses 31 transmitted through winding 17 are correspondingly varied, whereby the control wave e2 applied to the grid of power tube 1 is similarly varied and produces fluctuations in the amplitude of the space current impulse 33 transmitted by the power tube 1 to the oscillatory circuit 8, 9. It will be seen that the wave produced in the oscillatory circuit 8, 9 is under the control of the source 38 and varies in amplitude or in other Words, is modulated in accordance with the wave from source 38. The modulated waves in the circuit 8, 9 and output circuit 18 are suitable for transmission over a line circuit or'for radiation from an antenna in case the fundamental frequency of waves in the circuit'8, 9 is sufficiently high.

Fig. 4 shows a modification of the circuit illustrated in Fig. 1. The grid of power tube 1 is polarized with a highly negative potential by means of the condenser 50 and the grid leak resistance 51 operating in conjunction with the electromotive force e2 transmitted to the input circuit 2 from the auxiliary tube 11. The use of a high potential batter or generator 4 in connection with the grid o the power tube 1 is thus avoided, and at the same time a means is provided for automaticall maintaining the grid at the proper potentia The output circuit 3 includes the oscillatory circuit 8, 9 and the source of space current 52 shunted by the large capacity 53. Capacity 53 provides a low impedance path for the impulse 33 of space current and at the same time serves to shunt iiuctuations in the potential of the source of direct current 52. The oscillatory circuit 8, 9 is coupled by means of transformer 54 to an oscillatory work circuit 55, 56, 57, 58 which is tuned by means Aof variable capacity 56 to the same frequency as the oscillatory circuit 8, 9 that is, the frequency of oscillations to` be generated. Variable resistance 57 re resentsthe energy absorbing circuit or loa which is supplied with oscillations b the power tube 1. The input circuit 12 of the auxiliary tube 11 includes the condenser 59 shunted by the' grid leak resistance 60 to provide a high negative polarizing potential for the grid of auxiliary tube 11 and to take the place of a battery or similar source of potential 14 shown in Fig. 1. The input circuit 12 is coupled to the oscillatory circuit 55, 56, 57, 58 rather than tothe oscillatory circuit 8, 9 as in Fig. 1. The output circuit 13 of the tube l1 is provided with a source of space current 61 shunted by the large capacity 62 which functions in a manner similar to that described in connection with capacity 43. The circuit of Fig. 4 may be substituted in Fig. 1 for that portion of the circuit located on the right of switch 35. One lead of the substitute circuit is connected to conductor 36. The method of operation of the circuit of Fig. 4 is similar to that described in connection with Fig. 1. ACouplings 6, 54 and 15, 58 permit the values of el, e2, e3, e4 to be adjusted relatively to each other. If desired, the capacity 8 may be disconnected from the winding 9 by means of the switchl 63. In this case, the frequency of oscillations is determined -by the resonan frequency o f oscillatory circuit 55, 56,57, 5 It is obviously possible to employ other well known forms of coupling than those shown in Figs. 1 and 4 for linking the auxiliary and power tubes.

Although the invention has been described in yconnection with specific circuit modifications, in order to facilitate disclosure of the basic principles of the invention, it is obvious that the method of constructing and operating the circuit is not limited to the details shown. The features of the invention believed to be novel are set forth in the ap- 1. An amplifier of the space current type having an input and an output circuit, means for normally blocking the transmission of space current to said output circuit, wave dlstorting means, including a three-electrode space discharge tube, coupled to said input circuit for transmitting thereto periodically recurring non-sinusoidal impulses, and means for modulating the impulses transmitted to said input circuit comprising a modulator of the space current type havin an anodecathode circuit connected in s unt to the anode-cathode circuit of said wave distorting means.

2. An amplifier of the space current type having an input and an output circuit, means for normally blocking'the transmission of space current to said output circuit, wave distorting meanscoupled to said input circuit for transmitting t ereto periodically recurrin non-sinusoidal impulses, and means for mo ulating the impulses transmitted to said input circuit comprising a modulator of the space current type having an anode-cathode circuit connected in shunt to said wave distorting means, and a high frequency choke coil in said anode-cathode circuit.

3. An amplifier of the space current type having an input and an output circuit,.means for normally blockingv the transmission of space current to said output circuit, and means associated with said output circuit for translating a sinusoidal wave into a complex liier to cause said amplifier to produce oscilations, means in said feed-back circuit to distort the wave transmitted therethrough, and means associated with said feed-back circuit to modulate the waves transmitted by said feed-back circuit to said amplifier.

6. An oscillation enerator comprising an am lifier of the varlable impedance type, a fee -back circuit associated with said amplifier to cause said amplifier to produce oscillations, means in said feed-back circuit to distort the Wave transmitted therethrough, and means for applying modulating signals to said distortin means to modulate the output waves of sald generator.

7. An oscillation generator com rising an Y amplifier of the space current type aving an 'input circuit and an output circuit, ay relay circuit, means associated with said input cir cuits to normally prevent the transmission of an appreciable amount of space current to said output circuit and capacity and inductance associated with said amplifier output circuit to determine the frequency of oscillations generated.

8. In an amplifier of the variable impedance type having a discontinuous transmission characteristic, the method of amplif ing electrical oscillations at high efiiciency W ich comprises varying the impedance of said amplifier from maximum to minimum limits of said characteristic and vice versa in accordance with a Wave of more abrupt rate of chan e than a sine Wave of equal amplitude.

9. In an. amplifier of the variable impedance type having a discontinuous transmission characteristic, the method of amplifying electrical oscillations at high eciency which comprises distorting a sine wave to produce impulses of given amplitude having a higher rate of change than a sine Wave of equal amplitude, transmitting'said distorted Wave to said amplifier and varying the impedance of said amplifier between the limits of the transmission characteristic during that portion of the distorted Wave Which is near the maximumy peak and remote from the zero axis of said distorted Wave.

10. In an amplifier of the space current t pe, having a discontinuous transmission characteristic the method of amplifying elec-- trical oscillations at high efficiency which comprises producing an exciting Wave by amplifying. the peak of a sine Wave and suppressing the remaining portions of said sine Wave, normally blocking the space current transmitted by said amplifier and periodically neutralizing the blocking action in said amplifier under the control of that portion of the peak of said exciting wave which is remote from the zero axis of said wave.

11. In combination two relays, one of said relays comprising a space discharge tube, each relay having input and output circuits, the output circuit of each relay being connected to the input of the other to transfer energy thereto, and means for causing the wave form of the energy impressed by one relay upon the other to be steeper than a sine wave of equal amplitude.

12. A system comprisingy an` amplifier of the space current discharge type having an input and an output circuit, a Wave feed-back circuit associated with said amplifier to cause periodic discharges of current through said amplifier, means in said feed-back circuit to distort the Waves transmitted therethrough, and a capacity having a leak path in the input circuit of said amplifier for normally blocking the discharge of space current and the transfer of energy to said output circuit.

13. A system comprising an amplifier of the variable impedance type having an input circuit and an output circuit in which is produced sinusoidal waves, a feed-hackcircuit associated with said amplifier to supply Waves from s'aid output to said input circuit and means in said feed-back circuit including a space discharge path adapted to transmit a portion only of said sinusoidal Waves.

14. A system comprising an amplifier of the space current type, a feed-back circuit associated With said amplifier to cause said amplifier to have a regenerative effect, means in said feed-back circuit adapted to transmit a portion only of the impressed Waves, and means associated with said amplifier to selectively determine the frequency of Waves transmitted thro'ugh said feed-back circuit. In Witness'vvhereof, I hereunto subscribe my name this 26 day of March A. D., 1923.

HAROLD W. NICHOLS. 

